The present invention generally relates to telecommunication techniques. More particularly, the present invention relates to a method for providing a scheme for network users to manage their transmission powers and inter-sector interferences in uplink wireless communications. More specifically, embodiments of the present invention allows optimal allocation of uplink transmission power for each user with fair management of inter-sector interference in an Orthogonal Frequency Division Multiple Access (OFDMA) network. But it would be recognized that the invention has a much broader range of applicability.
The next generation of wireless networks will use OFDMA (Orthogonal Frequency Division Multiple Access) technology for a user attached with an access terminal (AT) in the uplink network communication. In OFDMA, the uplink resources assigned to a user are called tiles each of which consists of a subset of consecutive subcarriers. Since at most one user is assigned to each of these tiles then uplink transmissions within a sector are orthogonal or have no interference. However, the user AT transmission is still affected by inter-sector interference since other users in adjacent sectors may also have been assigned to the same tile. If those users in the adjacent sectors transmitted with high power then the inter-sector interference may severely limit the signal to interference and noise ratio (SINR) achieved by the user. Therefore, user transmission powers must be carefully managed to avoid excessive inter-sector interference.
For example, FIG. 1 illustrates a conventional method for dealing with transmission power adjustment for multiple users to achieve higher rates in the uplink of an OFDMA network. As shown, considering one of the users, and the user corresponds to a sector:
The transmission power of the user is increased for achieving a higher rate;
The interference caused by the user on adjacent sectors increases;
Users in adjacent sectors increase their powers to counter the increased interference and maintain their original rates;
The increased power of users in the adjacent sectors results in an increase in the interference in the sector;
The user must increase power to counter this increased interference; and
The sequence of events repeats until the user reaches its maximum transmission power.
Such an approach leads to a result that all users transmit with maximum power which is not an optimal use of uplink resources. Instead, system stability is better maintained by controlling user uplink transmission powers so as to maintain the interference at each sector within an acceptable range. In other words, in the uplink of an OFDMA network, the user AT transmission power must be chosen large enough to provide the desired rate for the user, but not too high to significantly degrade transmissions in neighboring sectors because of the interference caused to those transmissions.
In general, simply maintaining interference level within a set limit will not result in an optimal or fair solution. For example, consider a simple case of two sectors with two users. Even if only one user is transmitting, its rate is limited because of the limit placed on the interference it causes on the second sector. Clearly this is not optimal. Furthermore, suppose adding a third sector and that a user in that sector wishes to transmit. Then the user in the first sector is transmitting with sufficient power to cause the interference limit on the second sector to be reached. The third user then cannot transmit because doing so will cause the interference constraint for the second sector to be violated. This demonstrates that the system may not be fair. If the user in the third sector had instead started transmitting before the user in the first sector then the user in the first sector would similarly not be able to transmit. Hence the solution is non-unique and this may potentially result in instability.
Within a framework of the Third Generation Partnership Project 2 (3GP2), the inter-sector interference information is broadcast by sectors and can be used by ATs to adjust powers. Certain conventional techniques based on the framework for dealing the above problem are often not adequate for various reasons. For example, some central entity may require to collect all information associated with the AT transmissions and interferences, then compute the solution and inform each sector of this solution, or each sector must combine this information then determine an optimal solution. These conventional solutions require the exchange of a large amount of information and the delay in collecting this information may mean that the computed solution is no longer optimal when applied.
Therefore, an improved technique based on a distributed algorithm for providing optimal allocation of uplink transmission power is desired.